Position and assisted GPS

A Quectel LC76G receiver with an antenna inside the case tracks GPS, GLONASS, Galileo, BeiDou and QZSS at once. The position goes to the WiCAN PRO as its `gps_*` parameters, to the dongle's own Home Assistant link, and to the GPS page.

Receiver

Multi-constellation, one frequency band, a ceramic patch antenna on the board under the top of the case

First fix

Typically one to two minutes from cold with a view of the sky; faster with assisted GPS and a recent position

Assisted GPS

Off out of the box. A WiCAN PRO turns it on; on a computer, Agnss Enabled on the GPS page

Shows

The GPS page, the Status page's GPS tile, a breathing LED while it has a fix

Where to put the dongle

The antenna is a ceramic patch inside the case. It needs sky: the top of the dashboard, the rear parcel shelf, a spot under the windscreen, the dongle lying flat. Metal above it (a roof, a footwell under the dash) blocks the signal; glass does not, unless it is a metallised, heat-reflecting windscreen, which many cars have, and then the rear window is the better spot. A USB extension cable between the WiCAN PRO and the dongle is fine. If the fix is slow where you put it, try the dongle turned over: the patch radiates through one face of the case.

Reading the fix

GPS, with a fix. The page refreshes every 2 seconds.

Row	Meaning
Fix	Whether the receiver has a position, and the kind (3D with four or more satellites).
Quality	The NMEA fix quality: 0 none, 1 standard, 2 with SBAS corrections.
Satellites	Tracked (used in the fix) and in view (heard). A fix needs four tracked; more make it steadier.
Position, Altitude, Speed, Course	The last fix. Speed in km/h, course in degrees from north.
HDOP	The horizontal dilution of precision: a geometry figure, lower is better, under 2 is good.
Age	How long ago the receiver last reported. A growing age means the receiver stopped talking.

A WiCAN PRO shows the same on its USB › Status page and publishes gps_latitude, gps_longitude, gps_altitude, gps_speed, gps_heading and gps_satellites wherever vehicle parameters go. It only publishes a live fix; a remembered position is never reported as current.

Time to first fix

A cold start (no idea of the time, the orbits or the position) takes the receiver one to two minutes with a good view of the sky, sometimes longer in a car park. Three things shorten it:

• Assisted GPS (below): the dongle hands the receiver the time from the mobile network and the last known position, and the receiver predicts the satellite orbits itself for a few days ahead.
• A quiet USB cable. The host's USB transmitter sits close to the antenna, and a cable carrying data makes the receiver deaf to the weakest satellites. On the bench a cold fix took 86 to 110 seconds on a live USB link and 50 to 66 seconds with the data lines off. That is why the WiCAN PRO's WiFi modem mode cuts the lines, and why the WiCAN suggests that mode after ten minutes without a fix. See USB.
• The modem. Transmissions from the LTE modem disturb the receiver a little; Aic Enabled (active interference cancellation, on by default) is the receiver's own counter-measure.

Once it has a fix the receiver keeps it through a drive; it does not drop the fix when the modem transmits or when USB traffic starts.

Assisted GPS

With Agnss Enabled on, at every start the dongle:

1. waits for the time from the mobile network and injects it into the receiver;
2. injects the position it cached at the previous run (saved every Agnss Cache S seconds, 120 by default, while it had a fix);
3. lets the receiver's own orbit prediction (EASY) use that to find satellites at once. Epoc Constellation chooses which constellations the prediction covers: gps, gps_galileo (the default) or gps_bds.

A WiCAN PRO turns assisted GPS on when it pairs. agnss -s on the console shows the state (enabled, time injected, position injected, the cached position); agnss -e and agnss -d switch it for the next start.

Settings

GPS › Receiver Settings, applied with Submit Changes:

Enabled

Reserved. The receiver runs whenever the dongle does.

Agnss Enabled

Assisted GPS, off by default (a WiCAN PRO turns it on).

Agnss Cache S

10 to 86400 s, 120 by default: how often the position is cached for the next start.

Epoc Constellation

gps, gps_galileo or gps_bds: the constellations the orbit prediction covers.

Static Nav Threshold

0 to 20, in tenths of a metre per second, 5 by default: below this speed the receiver holds the position still and reports zero speed, so a parked car does not wander. 0 turns it off.

Aic Enabled

The receiver's active interference cancellation, on by default: the LTE modem transmits centimetres from the antenna.

Passthru

Advanced: at start, turn the USB console into a raw NMEA stream (for a GPS application on a computer). gps -t 1 does the same at runtime; typing seven + characters in a row brings the console back.

Uart0 Out

Advanced: copy the NMEA stream onto the dongle's UART.

Cli

Advanced: whether the gps and agnss console commands exist.

From the console

gps -p          the fix in one line (lat, lon, satellites, quality, altitude, HDOP, speed, course, age)
gps -p -j       the same as JSON, plus the assisted GPS state
gps -s          stream the raw NMEA sentences; any key stops
gps -c          check that the receiver is talking
gps -V          the receiver's firmware version
agnss -s        assisted GPS status

Troubleshooting

Symptom	Likely cause	What to do
No fix after two minutes	no view of the sky, or a live USB cable from a WiCAN PRO	move the dongle up and out; on a WiCAN PRO pick WiFi modem mode
No fix, ever, indoors	normal: the receiver needs the sky, a window at least	test it in the car
Fix, but the position jumps around while parked	Static Nav Threshold is 0	set it back to 5
Age keeps growing, the LED stops breathing	the receiver stopped reporting	gps -c on the console; a reboot restarts it
Satellites in view, none tracked	acquisition still in progress, or strong interference nearby	wait; try another spot
The WiCAN PRO shows no position although the dongle has a fix	the WiCAN reads only a live fix, over the cable or the access point	check the dongle's card on the WiCAN's USB › Status for the uplink state